This invention relates to an apparatus for collecting radiant solar energy and, more particularly, to a solar collector which optimizes the collection of direct and diffuse solar radiation and attenuates losses due to thermal convection, conduction, and reverse radiation.
Numerous systems have been proposed for the utilization of solar energy which generally comprise a collector unit which directs solar energy onto an energy-receiving means such as an evaporator unit or a conduit for a heat-exchange medium. In contradistinction to conventional fuel burning systems, the aforesaid solar devices provide a non-polluting source of usable energy. In one type of prior art system, large black aluminum collectors absorb the sun's energy beneath rigid sheets of transparent plastic. In such systems, a flat sandwich-like assembly is positioned to be aimed in the direction of the sun and tilted at an angle to collect the sun's rays. These prior art systems, while being useful, are generally excessively large and obstrusive for many conventional applications.
Other prior art systems have been suggested utilizing one or more reflector units which are mounted on a framework which changes its inclination corresponding to the elevation of the sun, thereby assuring that the reflected solar energy will always be directed at the energy-receiving means. Such systems impose severe restrictions on the size of the reflector assembly in that the assembly must be capable of swinging movement in a vertical plane.
Still other prior art systems have been suggested wherein frames carry a plurality of individually inclinable reflector units of parabolic cross-sections, with each reflector unit having its own energy-receiving means located at the focus of the parabola.
All such systems have limitations in that they either do not collect the diffuse or random incident rays from an overcast or cloudy sky, or they require a mechanism to adjust the collectors to the direction of the sun's rays which leads to troublesome maintenance and/or expensive components. All of the aforesaid units permit reverse radiation at times of a cold sky, i.e., at night, and also tend to lose heat by thermal convection and conduction.
More recently units have been suggested, for example, in U.S. Pat. Nos. 3,179,105; 3,229,682, and 3,923,039, which provide a significant improvement in collecting incident rays over the conventional focusing parabolic collectors which must track the sun, or flat plane collectors which cannot concentrate heat. However, the designs of the solar collectors in the aforesaid patents are cumbersome and/or expensive to manufacture and install, and/or cannot be fabricated on vertical or sharply inclined surfaces. Moreover, all permit reverse radiation as well as loss of thermal energy by convection and/or conduction.